1. Field of the Invention
The present invention relates to a speech synthesis apparatus for and a speech synthesis method of synthesizing a speech consisting of a plurality of speech segments each including at least one phoneme, and more particularly to a speech synthesis apparatus and a speech synthesis method which can synthesize a natural speech using a relatively small database capacity.
2. Description of the Related Art
In a conventional speech synthesis apparatus and a conventional speech synthesis method, a speech in a certain language is generally divided into a plurality of speech segments including at least one phoneme in the language. Further, each of the speech segments is generally disassembled into a plurality of pitch waveforms. The pitch waveforms obtained by disassembling each of the speech segments are associated with each of the speech segments and are registered in a database. The pitch waveforms in the database are used when the speech is synthesized.
One of such conventional speech synthesis method is disclosed in Japanese Patent Application Laid-Open Publication No. 171484/1998. In this conventional speech synthesis method, the pitch waveforms considered to be redundant are removed for the purpose of saving capacity of the database, and the other pitch waveforms as representatives are used to synthesize the speech.
The conventional speech synthesis method stated above, however, encounters such a problem that the database cannot store the pitch waveforms with data significantly reduced by the reason that the pitch waveforms vary in shape due to differences in their phase characteristics before synthesizing a natural speech. Another problem is that the less number of the pitch waveforms to be registered in the database for saving capacity of the database, the lower sound quality of the synthesized speech.